The present invention relates to a method for forming a fine pattern of a semiconductor device using an immersion lithography process.
Due to increased integration of semiconductor devices, improvement of technologies for forming a fine pattern of sub-micron has been required, and research for developing photolithography processes have been accelerated to achieve integration of circuits in the semiconductor manufacturing process.
In a conventional photolithography process, light sources such as g-line (436 nm) and i-line (365 nm) are used as exposure light sources. Recently, KrF (248 nm) and ArF (193 nm) which are light sources of a Deep Ultra Violet (DUV) region and F2 (157 nm) and Extremely Ultraviolet (EUV) (13 nm) which are short wavelength light sources have been applied to the manufacturing process.
Since new light sources require development of a new exposer, it is costly in terms of manufacturing cost. Also, it is difficult to manufacture a highly-integrated semiconductor device having a fine pattern because the resolution of the pattern obtained from the exposer equipment using a short wavelength light source is limited to 0.1 μm
Instead of a dry exposing process, an immersion lithography process has been applied to the device manufacturing process. The immersion lithography process uses a system comprising a solution between an exposure lens and a wafer to perform an exposure process. Since the immersion lithography process is performed with a solution having a refractive index between the photoresist film and the exposure lens as a medium, a hyper NA (numerical aperture) lens can be embodied corresponding to a refractive index of water to the air, thereby increasing the resolution of the lithography process. There is also no decrease in the depth of focus so that it is possible to form an ultra-precision pattern having a small pitch.
Since the medium used in the immersion lithography process is a solution such as water having a high specific heat, a part of the solution remains over the pattern which can generate a water mark effect having a circular bridge type or a bubble after a drying process. Furthermore, contaminant is eluted from the photoresist film to the medium (solution) to contaminate the contacted exposure lens.